This invention relates to a light-emitting device and a material therefor. More particularly, it relates to a light-emitting device having high brightness, high luminescence efficiency, and excellent durability.
Various light-emitting devices have now been intensively researched and developed. In particular, organic electroluminescent (EL) devices are attracting attention as promising light-emitting devices that emit light with high luminescence brightness at a low voltage. For example, an EL device having an organic thin film formed by vacuum evaporation of an organic compound is known (Applied Physics Letters, vol. 51, p. 913 (1987) ). This device comprises a laminate of tris(8-hydroxyquinolinato)aluminum (Alq) as an electron-transporting material and an amine compound as a hole-transporting material to exhibit markedly improved EL characteristics over conventional single layer type devices.
Application of an organic EL device to color displays have recently been studied. Before a high performance color display can be developed, it is necessary to improve light emission characteristics each of blue, green and red light.
Applied Physics Letters, vol. 75, p. 4 (1999) reports a green light-emitting device which makes use of light emission from an iridium complex for improving light emission characteristics. The device reported achieves an external quantum efficiency of 8%, which is higher than the 5% level that had been regarded as an upper limit that could be reached by predecessors. However, it has insufficient durability, still needing improvement.
Of organic light-emitting devices, while it is those having an organic substance deposited by vacuum evaporation that accomplish high brightness light emission, it is desirable to make a device by a coating method from the standpoint of simplification of production process, processability, and increase of a display area. However, light-emitting devices prepared by general coating methods are inferior to those prepared by vacuum evaporation in luminescence brightness and efficiency, which has been an outstanding problem waiting for solution.
An object of the present invention is to provide a light-emitting device which provides high brightness and high light emission efficiency and has excellent durability.
The object of the invention is accomplished by the following means.
(1) A light-emitting device comprising:
a pair of electrodes formed on a substrate; and
organic compound layers comprising a light-emitting layer provided in between the electrodes,
wherein at least one of the organic compound layers comprises a heterocyclic compound having at least two hetero atoms and a phosphorescent compound.
(2) The light-emitting device according to (1) above, wherein the phosphorescent compound is an organic metal complex.
(3) The light-emitting device according to (2) above, wherein the organic metal complex is an ortho-metalated metal complex.
(4) The light-emitting device according to (1) above, wherein the heterocyclic compound is represented by formula (I): 
xe2x80x83wherein R represents a hydrogen atom or a substituent; X represents xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x95x90Nxe2x80x94 or xe2x95x90Nxe2x80x94Ra; Ra represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group; and Q represents an atomic group necessary for forming a hetero ring together with N and X.
(5) A polymer comprising a repeating unit represented by formula (D-I): 
xe2x80x83wherein ArD represents an arylene group or a divalent heterocyclic group; RD1 and RD2 each independently represent a hydrogen atom or a substituent; nD represents an integer of 0 to 3; and mD represents an integer of 0 to 5.
(6) The light-emitting device according to (1) above, wherein the heterocyclic compound is a polymer comprising a repeating unit represented by formula (D): 
xe2x80x83wherein ArD represents an arylene group or a divalent heterocyclic group; RD1 and RD2 each independently represent a hydrogen atom or a substituent; nD represents an integer of 0 to 3; mD represents an integer of 0 to 5, and mxe2x80x2 represents 0 or 1.
(7) The light-emitting device according to (6) above, wherein the substituent is a group selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkoxy group, an aryloxy group, an acyl group, a halogen atom, a cyano group, a heterocyclic group, and a silyl group.
(8) A polymer comprising a repeating unit represented by formula (E-I): 
xe2x80x83wherein ArE represents an arylene group or a divalent heterocyclic group; RE1 and RE2 each independently represent a hydrogen atom or a substituent; nE and mE each independently represent an integer of 0 to 5.
(9) The light-emitting device according to (1) above, wherein the heterocyclic compound is a polymer comprising a repeating unit represented by formula (E): 
xe2x80x83wherein ArE represents an arylene group or a divalent heterocyclic group; RE1 and RE2 each independently represent a hydrogen atom or a substituent; nE and mE each independently represent an integer of 0 to 5; and nxe2x80x2 represents 0 or 1.
(10) The light-emitting device according to (9) above, wherein the substituent is a group selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkoxy group, an aryloxy group, an acyl group, a halogen atom, a cyano group, a heterocyclic group, and a silyl group.
(11) The light-emitting device according to (3) above, wherein the ortho-metalated metal complex is an iridium complex.
(12) The light-emitting device according to (1) above, wherein the organic compound layers comprise a polymer.
(13) The light-emitting device according to (1) above, wherein the phosphorescent compound has a phosphorescence quantum yield at room temperature of at least 25%.
(14) The light-emitting device according to (3) above, wherein the ortho-metalated metal complex contains 5 to 100 carbon atoms.
(15) The light-emitting device according to (3) above, wherein the ortho-metalated metal complex is a compound having a partial structure represented by formula (K-1): 
xe2x80x83wherein M represents a transition metal; Qk1 represents an atomic group necessary for forming a 5- or 6-membered aromatic ring; and Qk2 represents an atomic group necessary for forming a 5- or 6-membered aromatic azole ring;
or tautomer of the compound.